This invention relates to the assembly of semiconductor devices, and more particularly to the assembly of semiconductor devices including the process of etching aluminum foil which invention more particularly relates to the process of cleaning the aluminum foil prior to the aluminum etch in preparation for such assembly process.
As will be understood by reference to the foregoing related patent applications in the assembly of semiconductor devices, it is necessary to prepare an aluminum foil by etching of bonding fingers therein for assembly to a semiconductor chip and to a lead frame for encapsulation. The aluminum foil utilized in such process is typically made by reducing thick ingots to foil in a rolling mill operation. To accomplish this, several types of cutting oils and lubricants are used to aid the rolling process. In some cases, heat is also employed. As a result, the surface of the foil is covered and embedded with a greasy, oxide mixed, rolled scored surface. Since the etch strip process requires coating of the foil with a photoresist, the greasy oxide, rolled scored surface of the foil is difficult to coat in good quality with the photoresist. The photoresist must have sufficient adhesion to undergo the further processing, i.e., align and expose, acid etch, etc., to define the lead properly for the etch strip assembly process. If the aluminum surface is not properly cleaned prior to the application of the photoresist, blisters, poor adhesion and brittleness of the photoresist results.